ACTG 372 - The overarching rationale for ACTG372 is to explore relevant scientific questions while examining new treatment options for prior ACTG320 participants (and a limited no. of non- ACTG320 volunteers, if needed) who have been receiving ZDV(or d4T)+3TC+IDV and are currently exhibiting a range of virolic responses. By dividing the study in to the corresponding, non-sequential cohorts (Groups A,B,C,D) different approaches to evaluating virologic success and virologic failure can be explored.